HOCRTextBox.h

/*
 * Copyright © 2016--2018 Stefan Kebekus <stefan.kebekus@math.uni-freiburg.de>
 *
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
 
#ifndef HOCRTEXTBOX
#define HOCRTEXTBOX 1
 
#include <QPainter>
#include <QSet>
#include <QXmlStreamReader>
 
#include "resolution.h"
 
class HOCRDocument;
 
 
class HOCRTextBox
{
 public:
  HOCRTextBox();
 
  bool hasText() const;
  
  qreal angle() const {return _angle;};
  
  QXmlStreamAttributes attributes() const {return _attributes;};
  
  QVector<qreal> baselinePolynomial() const {return _baselinePolynomial;};
  
  QPoint baselineReferencePoint() const {return _baselineReferencePoint;};
  
  QRect boundingBox() const {return _boundingBox;};
 
  QString classType() const;
 
  int confidence() const {return _confidence;};
 
  QString direction() const {return _direction;};
 
  qreal fontSize() const {return _fontSize;};
  
  QString imageName() const {return _imageName;};
 
  QString language() const {return _language;};
 
  void render(QPainter &painter) const;
 
  QImage toImage(const QFont &overrideFont, QImage::Format format=QImage::Format_Grayscale8) const;
 
  QByteArray toRawPDFContentStream(const QFont &font, resolution xRes, resolution yRes, length deltaX=length(), length deltaY=length()) const;
 
  QString toText() const;
  
  qint64 estimateFit(const QFont &font) const;
    
  QFont suggestFont() const;
  
  QString text() const {return _text;};
 
 private:
  // Specifies how and where the textbox' content should be drawn.
  struct renderingHints {
    int fontSize;
 
    QPoint referencePoint;
 
    qreal horizontalStretchFactor;    
  };
 
  // For a given font, this method computes rendering hints so that the text
  // fits the bounding box best.
  //
  // - If the HOCR file specifies a font size, this size is taken. Otherwise,
  // - the font metric is used to find a size that best fits the bounding
  // - box. As a last resort, a standard value is returned.
  //
  // - The font metric is used to suggest a point from which to draw the text of
  // - this text box, and a horizontal stretch factor
  renderingHints getRenderingHints(const QFont &font) const;
 
  // This is to ensure that text boxes can be constructed from HOCR documents.
  friend HOCRDocument;
  
  // Constructs a textbox by reading in an xml file. This constructor expects
  // that the QXmlStreamReader points to a start element.  It will read the file
  // until it reaches the corresponding end element.  When the method returns,
  // the QXmlStreamReader points to this end element.  In case of problems,
  // warnings are added to 'warnings'.
  HOCRTextBox(QXmlStreamReader &xml, QSet<QString> &warnings, HOCRTextBox *parent=0);
 
  // Interprets _attributes and fills in the members _baseLine, _boundingBox,
  // _class, _confidence, _fontSize, _imageName.  Problems encoutered in the
  // interpretation are added to the set 'warnings'.  This method is called only
  // in the constructor.  The code is not part of the constructor to keep the
  // source readable.
  void interpretAttributes(QSet<QString> &warnings, qint64 line, qint64 column);
 
  // Attributes, as read from the HOCR file
  QXmlStreamAttributes _attributes;
 
  // List of sub boxes, as read from the HOCR file
  QList<HOCRTextBox> _subBoxes;
  
  /*
   * Attributes extracted from the HOCR file
   */
 
  // Textangle, as specified in the HOCR file or inherited from parent. If no
  // angle was specified, this number is zero.
  qreal _angle;
  
  // Base line as a polynomial, as specified in the HOCR file or inherited from
  // parent. If no base line was specified, this vector is empty.
  QVector<qreal> _baselinePolynomial;
 
  // Base line reference point, as specified in the HOCR file or inherited from
  // parent. If no base line polynomial is specified, this member is
  // meaningless.
  QPoint _baselineReferencePoint;
 
  // Bounding box, as specified in the HOCR file. If no bounding box was
  // specified, this box is empty.
  QRect _boundingBox;
  
  // Contains the class of the corresponding element in the HOCR file. Typical
  // values are "ocr_page", "ocr_carea", "ocr_par", "ocr_line" or "ocrx_word".
  QString _class;
 
  // Contains the confidence level of the corresponding element in the HOCR
  // file.  If no confidence level is specified, this member contains '-1'.
  int _confidence;
  
  // Contains the text flow direction of the corresponding element in the HOCR
  // file.  The value 'ltr' means left-to-right, 'rtl' means right-to-left.  Any
  // other value means 'undefined'.
  QString _direction;
  
  // Contains the font size specified in the corresponding element in the HOCR
  // file.  If no font size is specified, this member contains '0.0'.
  qreal _fontSize;
 
  // Contains the name of an image associated with the content of this text
  // box. If nothing is specified in the HOCR file, this string is empty.
  QString _imageName;
 
  // Language of the content of this text box. If nothing is specified in the
  // HOCR file, this string is empty.
  QString _language;
 
  // Contains the text of this text box. If nothing is specified in the HOCR
  // file, this string is empty.
  QString _text;
 
  /*
   * Helper functions
   */
  
  // Expects a string of the form "blabla int int int …" and returns a vector
  // containing the integers
  QVector<int> getIntegers(const QString& spec) const;
 
  // Expects a string of the form "blabla qreal qreal qreal …" and returns a
  // vector containing the qreals
  QVector<qreal> getFloats(const QString& spec) const;  
 
  // Trivial method that writes out a floating point number in ASCII, up to four
  // decimal points of precision. Trailing zeroes are deleted for brevity's
  // sake. It seems that Qt cannot do that
  QByteArray toNumber(qreal x) const;
 
  // Internal method that actually does the work for the user method with the
  // same name.  This method is applies recursively over all sub-boxes, and the
  // results are joined. It differs from the user method in that it takes two
  // additional arguments: 'height' is the height of the bounding box for which
  // the user method was called; this is necessary for correct text
  // placement. The argument "currentSize" is the font size last set; this is
  // used to set and re-set the same sizes times and again. The parameter
  // 'codec' is a pointer to the "Windows-1252" QTextCodec.
  QByteArray toRawPDFContentStream(const QFont &font, resolution xRes, resolution yRes, length deltaX, length deltaY, quint16 height, qreal &currentFontSize, QTextCodec *codec) const;
};
 
 
#endif